1. Field of the Invention
The present invention relates to methods for guiding aquatic crustaceans' locomotive orientation with their innate biological tendency responding to specific contrasts of bright and dark. This visual effect of bright and dark contrasts is generated at a predetermined area within these crustaceans' residing water body to attract their move toward the predetermined areas for staying or hiding.
2. Description of Related Art
Aquatic crustaceans are important economic aquatic animals. People usually obtain those animals by harvesting them from nature environments directly or by artificial cultivation. Many countries have paid great attention on their artificial cultivation as a business named aquaculture. Traditional aquaculture makes use of wide expanse of land and ponds with natural water supply. Only recently, several high-density culture systems have been disclosed. These systems use water recirculation equipments including filtration apparatuses to curtail both the consumption of water and land resources resulting in less damages to natural environments, like U.S. Pat. Nos. 4,368,691, 4,446,025 and 5,961,831. High-density cultivation systems bring larger profit margins but simultaneously increase the production loss resulting from cannibalization of animals densely living in the systems. This loss is derived from differences in size and living stage of cultured animals, ex. newly molted or immature crustaceans are usually vulnerable to predation of their none-molted and/or larger mates within the same body of water. This is the bottleneck in the efforts to elevate the culture density and hence to increase profits as well.
Cannibalism-avoiding behavioral management is thus an important task for maintaining cultivated aquatic crustaceans in above-said high-density systems. For that purpose, spatial separation of molting and none-molting crustaceans is one way to avoid molted animals from being predated. Several means to attract aquatic crustaceans' active moving can be employed in attempting to lure none-molting animals to stay away from molted ones. For example, traditional pond culture or tank culture uses deep water and wide space to passively reduce the contact between newly molted and none-molted crustaceans. In addition, scent/taste attractants and chemo-attractants are used to manage crustacean's displacement over feeding, breeding and hatching. U.S. Pat. No. 5,706,759 discloses a process to investigate potential chemo-stimulants, chemo-repelling agents or chemo-attractants for shrimp, but this invention still lacks further practical techniques for behavioral management in high-density culture. A kind of bait fluids, such as the fish oil, is used in U.S. Pat. No. 4,828,829 for harvesting crab only with expected higher efficiency. A food-luring trapper holding collected plankton or other similar shrimp food organisms is designed to allure and catch shrimp (U.S. Pat. No. 5,259,809). No other successful methods for managing the motion of aquatic crustaceans in light of their biological responses reacting to bright and dark visual stimuli have been developed previously.
Due to lack of proper techniques for fully managing aquatic crustaceans in high densities, the newly developed re-circulation systems have culture densities always maintained as a balance between cannibalization and growth, and, in shrimp, the culture pond or tank is always kept in certain water depth, about 0.6 to 2.0 meter, in order to reduce the incidence of cannibalizing behavior basing on the behavior that newly molted shrimp jump back or up away in order to escape from the attack of other none-molted shrimp mates. The culture water body with the depth of 0.6 to 2.0 meters has too large a mass to enable the development of multi-layered culture system and thus the traditional culture system is restricted to a planar installation.
In other fields, laboratories with crustaceans cultivated in controlled environments for research and markets like restaurants with crustaceans kept in tight space for display all face the same problems in behavioral management of aquatic crustaceans and are unable to maintain or display living crustaceans effectively in desired manners.
In nature, many aquatic crustaceans, such as shrimps, inhabit in water environments with bright-dark alternating or contrasting light effects appearing as wavy light reflections in shelters and crevices but not in open fields. Crustaceans may use these light effects to aim for a potential hiding place. Once arriving to the location, they may use their other senses to decide if they would take the action of hiding or go for another potential location.
Propensity for aquatic crustaceans to react to the bright and dark visual stimuli is a unique nature which can be used as a feasible means to guide their motion and localization. The present invention for guiding the displacement of aquatic crustaceans is centered upon the aforesaid biological tendency. This tendency responding to bright and dark contrast of crustaceans is not unique as it can be found in other animals, like insects. No practical concepts in the prior art, however, are disclosed as an efficient and effective process for guiding aquatic crustaceans' motion related to the techniques used in the present invention.